Idles at 500 RPM, noticeable vibration

[ta240]

My 2013 CX-5 has about 340,000 miles on it. In the last few months I've noticed a tendency for it to drop to around 500 RPM when stopped in gear and the a/c off. When it does that, I can feel vibration from the engine. If I give it just a tiny bit of gas to bring it back up to to 600ish then it smooths right out.

Sometimes for the first 45+ minutes of driving it will idle back where it used to, in the 600-650 range, and then it is so smooth I can't really tell it is running when I stop at a light. Once it goes to the lower idle it doesn't usually go back up until it has sat for hours.

Over the last 75,000 miles or so, I've used the sprays to help with the carbon buildup after getting the error code indicating that problem. I had Iridium spark plugs in it and tried the NGK Ruthenium ones recently and on shorter drives it seemed to help but on longer ones it still goes to the slower idle. It never burns any oil, doesn't have any error codes and I only run top tier gas in it.

Suggestions on what to look at?

 

[N7turbo]

That's a lot of miles. It might be time for a full walnut blasting of the cylinder head, and a MAF and TB cleaning as well.

 

[ta240]

I figured the sprays are only cleaning enough of the buildup on the valves to keep it from getting error codes so a full cleaning would be a good idea.
Spraying the valve cleaner in before the TB has it looking really spotless but a MAF sensor cleaning is a good idea.

 

[GFrosty]

This past year, on my own CX-5 I also had stumbling along with a few instances of "random misfire" (P0300) codes thrown. After replacing the spark plugs (it was almost time), and tracking down a spark coil issue (new coils), along with several tanks' worth of fuel system cleaner, I haven't had the issue since. Hasn't always had top-tier gas, but does now.

But this Spring, I'll begin going through all of the various emissions and vacuum hoses, sensors and valves to ensure they're all clean and test-out as properly functioning. At 135Kmi, it's worth my time to have a few weekend futzing-sessions that help me get to know the car better and to track down any latent/building issue that might have been contributing to the low-idle and stumbling condition I'd had.

And I have yet to to the "walnut shell" cleaning of the valves, which many report as helping with erratic performance. Might get that done this coming year, as well.

At 300Kmi+, IMO it's worth considering all of the sensors and valves that have to do with vacuum, emissions, air/flow sensing.

PCV valve
Vapor Canister Purge Solenoid (AKA, Evap Purge Solenoid or Purge Valve Solenoid)
IAT temperature sensor
EGR valve
Vacuum hoses

If not getting codes by the ECU, it's likely some of those have zero issues at all. But it might be worth a cleaning and check, with some of them. Shouldn't require any parts purchases, unless they're showing clear signs of failure even after cleaning.